1. Technical Field
This invention relates to the continuous production of linear, secondary aliphatic alcohols, with co-production of carboxylic acid esters, from selected olefins, alcohols and carboxylic acids. This is achieved by two reactions in sequence: (1) the reaction between .alpha.-olefins and carboxylic acids, and (2) a transesterification reaction.
2. Description of the Prior Art
The oxylation of olefins by carboxylic acids has long been known in general terms: however, catalysis has been problematical and full commercial success has been elusive. More specifically, homogeneous, strong acid catalysis of the olefin/carboxylic acid reaction is well known (see U.S. Pat. Nos. 2,414,999 and 2,415,000), but suffers from problems of poor efficiency and troublesome product isolation attributable to extensive by-product formation through olefin dimerization and oligomerization reactions (cf. Rohm & Haas Co. Technical Bulletin entitled "Amberlyst.RTM. 15, "Fluid Process Chemicals Group, Sept. 1978). Furthermore, since the equilibrium constant for the olefin/carboxylic acid addition reaction decreases rapidly with increasing chain length of the olefin (cf. U.S. Pat. No. 3,037,052), this reaction has generally been considered impractical for olefins in the detergent range of C.sub.11 -C.sub.16. Attempts have been made to overcome the problems inherent with homogeneous catalysis by using heterogeneous catalysts of the strong acid type, such as sulfonated styrene/divinyl benzene copolymers. However, the gel-type ion-exchange resins were ineffective catalysts for the reaction, whereas the macroreticular type resins were effective catalysts for the reaction with .alpha.-olefins, but not for the reaction with the internal olefin species which are formed during the reaction by isomerization.
One object of the present invention, therefore, is to provide for the efficient catalysis of the reaction between certain .alpha.-olefins, and their internal isomers, and certain carboxylic acids.
Transesterification and reactive distillation are each individually known in a variety of processes. Transesterification is virtually always practiced as a batch reaction with rather large quantities of one reactant being used to drive the reaction toward completion by mass action displacement of the equilibrium.
Another commonly used approach is that of equilibrium displacement by removal of product or coproduct as it is formed in the system; frequently this can be accomplished via an azeotropic distillation. Continuous transesterification has been practiced, but in only few instances and then only under circumstances decidedly favorable to the reaction. For example, one system has been described for continuously ester-exchanging 1,4-butanediol diaacetate with methanol to coproduce 1,4,-butanediol and methyl acetate (cf. German patent application No. 2,820,521 to BASF-AG or British patent application No. 2,031,421 to Japan Synthetic Rubber). A second system (cf. U.S. Pat. No. 4,260,813 to Showo Denko K.K.) has been described for continuously producing ethylene glycol monoethyl ether acetate from ethylene glycol monoethyl ether and ethyl acetate. In both of these systems, conditions for exchange are favorable because the esters being exchanged are derived from reactive primary hydroxyl groups. A particularly significant attribute of the prior art systems, however, is that they need not react to substantial completion because the higher molecular weight alcohol and ester couples used as reactants can be separated by conventional distillation. Such separation is not possible in the systems of the present invention because the acetate esters of typical detergent range alcohols, such as the tridecyl and tetradecyl alcohols, boil at the same temperature as the corresponding alcohols, and the downstream conversion of the product secondary alcohols, into high-performance surfactant-range alcohols requires substantially pure alcohol reactants.
Thus, another object of the present invention is to provide for the efficient transesterification of the reaction products of olefins and carboxylic acids to produce desired alcohols and by-product carboxylic acid esters.
Both reactions employed in this process are chemically reversible; i.e., under usual conditions they reach equilibrium at a point short of complete conversion. Generally speaking, such reactions are not well-suited to multi-step, continuous process operation; that two such reactions are employed in the continuous process of this invention is, therefore, unique in itself. Moreover, both reactions exhibit certain other characteristics which under the usual circumstances would render them unattractive candidates around which to develop a continuous process. For example, the carboxylic acid/ .alpha.-olefin reaction of step (1), above, is generally considered to present problems of (1) decreasing equilibrium constant with increasing size of olefin, (2) by-product formation (efficiency loss) through olefin oligomerization/polymerization, and (3) poor structural selectivity in the product (multiplicity of positional isomers, all secondary are formed) because of olefin isomerizations which accompany the desired acid/olefin addition reaction. Accordingly, this reaction would not generally be considered an attractive choice for inclusion in a continuous process route to long-chain alcohols. Similarly, the transesterification reaction of step (2), above, is generally considered to be useful only in cases where (1) incomplete conversions are acceptable, (2) large excesses of one reactant may be used to drive the reaction in the desired direction, or (3) the equilibrium position can be displaced by continual removal of either product or coproduct. Thus transesterification, although generally a clean, efficient reaction, is typically practiced only as a batch operation.
Accordingly, an additional object of the present invention is the development of an economically superior, highly efficient, environmentally clean, continuous process utilizing the reaction sequence described above.